For single- or multi-color printing of a recording medium, for example of a single sheet or of a belt-shaped recording medium made from the most varied materials (for example plastic, paper or thin metal foils), it is known to generate image-dependent potential images (charge images) on a potential image carrier (for example a photoconductor), to ink these potential images in a developer station (inking station) and to transfer-print the image so developed onto the recording medium.
Either dry toner or liquid developer can thereby be used to develop the potential images.
A method for electrophoretic liquid development (electrographic developing) in digital printing systems is, for example, known from EP 0 756 213 B1 or EP 0 727 720 B1. The method described there is also known under the name HVT (high viscosity technology). A carrier fluid comprising silicon oil with ink particles (toner particles) dispersed therein is thereby used as a developer fluid. The toner particles typically have a particle size of less than 1 micron. Something close to this can be learned from EP 0 756 213 B1 or EP 0 727 720 B1, which are components of the disclosure of the present application. Described there are electrophoretic liquid developing methods of the cited type with silicon oil with toner particles dispersed therein as a carrier fluid and additionally a developer station made up of one or more application rollers for wetting the potential image carrier (developer roller) with liquid developer corresponding to the potential images on the potential image carrier. The developed potential image is then transferred onto the recording medium via one or more transfer rollers.
In order to secure the toner images in the recording medium, these are fixed in a fixing station.
The disadvantages of the known fixing methods are to be seen in the following points:
1.) Dry Toner Printing:                Here thick toner layers are used, therefore a high fixing energy requirement is required with significant paper stress given heat fixing or heat/pressure fixing; the abrasion of fixed dry toner layers in the printer and in the post-processing is frequently problematic.        
2.) Liquid Toner on the Basis of Volatile Carrier Fluids:                The carrier fluid is afflicted with odor and flammable, residues of carrier fluid remain on the recording medium, the evaporation time lies in the range of multiple seconds or, respectively, minutes, tendency to smear exists.        
3.) Liquid Toner, Water-Based:                Danger of the discharge of an electrostatic charge image in contact with the conductive liquid exists (U.S. Pat. No. 5,943,535), evaporation of the residual water on the recording medium is not possible in very short time spans given temperatures that are not too high, the optimization with regard to complete transfer is problematic.        
4.) Liquid Toner, Silicon Oil-Based:                Fixing on non-porous or non-silicon oil-absorbing substrates is problematic.        
5.) Conventional Printing Methods:                No variable print form is possible, the edition 1 or low print run is uneconomical.        